This invention relates to automatic test equipment for testing optical systems and more particularly describes a system for automatically determining the optical characteristics of any optical test object by directing laser beams through the lens elements and measuring the exit points, slopes and intensities of the reflected beams.
Test apparatus for optical systems may be thought of as being divided into two types, those that measure the parameters of the human eye and those that measure the parameters of man-made optical systems. One well known apparatus for the examination of the eye is an ophthalmoscope. This instrument is used primarily to view the internal parts of the eye, but also can be used as a rough measure of the eye lens refractive power, in that the degree of adjustment of the ophthalmoscope lens to bring the subject's retina into focus is also a measurement of the refractive power of the patient's eye lens. The refractive power of a medium is a measure of the amount of deflection from a straight line undergone by a light ray in passing obliquely through the medium. In the eye, it is a measure of the distance between the lens and the focal point, and determines near or far-sightedness. The accuracy of the ophthalmoscope for determining the refraction is limited. Thus, an accurate measurement of a patient's eye is not practically obtainable with an ophthalmoscope.
Retinoscopes are used in conjunction with refractors to determine the refractive condition of the eye but the test results are approximate and require an operator of skill, and patience on the part of the subject.
Because of the shortcomings of these and other standard equipment and techniques now available, the most common method of determining the refractive condition of the eye is the subjective one where the subject views a variety of targets through various lenses and decides which set of lenses produces the clearest image. This method is, of course, time consuming and subjective on the part of both the patient and the operator. Further, the equipment operator does not know what is actually being seen by the patient.
In the case of man-made optical systems, a variety of equipment is also available. In one test apparatus, a collimated light beam is directed towards the entrance pupil and the light which is found to be emanating from the other side of the lens is collected and analyzed to determine the optical characteristics of the test object. This technique can be used with single lenses and multi-element lenses if the image space is accessible. Sometimes, however, it is inconvenient to access the image space.
Another method is to analyze the differences in images formed by the test device when its entrance pupil is only partially illuminated.
The methods mentioned above are time-consuming, require considerable expertness, and suffer from poor signal to noise characteristics. Various interferrometric techniques are also employed but these are less popular because of their sensitivity to environmental perturbations and the requirement for even greater operator expertness.
What is required by the optical industry is a compact, economic test apparatus for determining the optical characteristics of any test object, including the human eye, which can be used automatically to test the optical characteristics of the test object in a minimum amount of time.